Fir has two fresh water pumps and two fire pumps. These pumps check out (electrically and practically) and there appears to be no reason to replace them.
Supply to Water Production
We need a new pump to move water from the stern sea chest through the initial water filters. This pump is at least 6 feet below the water line so the pump does not have to self prime. While the source water passes through a strainer, the source could include suspended solids like sand, silt, and mud. We are not looking for a true "trash" pump but we want a pump that can deal with sand. This will be a relatively low pressure, single stage centrifugal pump. The pump ought to produce at least 5 gallons per minute after accounting for pressure loss from the sediment filters.
Supply to Domestic Water System
The existing domestic water pumps ought to be replaced. The original pumps (3 phases 440 volts) are old. One has been disconnected. The pressure transducer on the other has an obvious problem. The previous owner rigged in a 110 volt well pump attached with PVC piping which is clearly not up to the task.
As with every other part of the boat, the challenge is to build a system that can be scaled for a variety of uses. With a few people on board, we probably need around 5 gallons per minute of flow. This will take care of a couple of showers, sinks, toilets, etc. At peak, we want to handle about 30 gallons per minute which is driven by our need to wash down the boat without losing pressure for domestic services. We want the system to maintain 70lbs. of pressure and our existing 250 gallon pressure tank should provide enough of a buffer. Since this is a critical system, we want two pumps. One solution we will explore are synchronized, variable drive, multi-stage pumps. The idea is that these pumps only run as quickly as is require to maintain the pressure at a given rate of flow. So, one pump may run at a given speed to maintain 70 lbs at 5 gallons per minute. The system may use two pumps at a higher speed to maintain 70 lbs at 30 gallons per minute. Variable drive technology is mature and is common in industrial applications.
Check back to see what pumps we selected.